Juvenile hormone and aggression in honey bees

We determined whether defense by individual bees against non-nestmates in h oney bees (Apis mellifera) is correlated with their juvenile hormone (JH) t iters, which are known to vary developmentally and seasonally. We bioassaye d winter and summer bees for aggressive and non-aggressive individuals. Bee s in winter could not be distinguished by task group, but bees in summer we re segregated into nurses and guards. JH titers were correlated with aggres sive behavior at two levels. First, winter bees and summer nurses, known to have lower JH titers, both showed less aggression toward foreign bees than did summer guards. Second, aggressive individuals had significantly higher JH titers than did non-aggressive bees within each colony. Inter-colonial variation in aggressiveness was maintained during summer and winter, sugges ting a genetic basis for these differences. An alarm pheromone test further substantiated the existence of inter-colonial differences. We found signif icant variation in JH titers among different colonies, but this variation w as not significantly associated with colony-level aggressiveness. The corre lation between JH and levels of aggressiveness within a colony suggests a r egulatory role for JH, but variation among colonies involves factors other than JH. (C) 2001 Elsevier Science Ltd. All rights reserved.